Methods and apparatus for wireless network connectivity

ABSTRACT

Methods and apparatus which allow a wireless terminal ( 302 ) to simultaneously maintain connections with multiple base stations ( 304, 306 ) are described. Each wireless terminal ( 302 ) is capable of supporting multiple separate timing and/or other control loops one, for each base station connection thereby allowing the connections to operate independently and in parallel. Different control signals and/or data are transmitted on each connection that is established with a base station ( 302, 306 ). In this manner base stations ( 302, 306 ) receive different data allowing for asynchronous data transmission. The data received by the base stations ( 302, 306 ) can be supplied to a wired asynchronous network ( 308 ) without the need to combine the received data prior to supplying it to the wired network ( 308 ). The communications techniques of the invention can be used to implement soft handoffs without the need to duplicate data transmissions to multiple base stations.

RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 10/217,791 filed Aug. 13, 2002 titled, “METHODS AND APPARATUSFOR WIRELESS NETWORK CONNECTIVITY,” now allowed, which claims thebenefit of the filing date of U.S. Provisional Patent Application Ser.No. 60/312,126 filed Aug. 14, 2001 titled: “A METHOD FOR PROVIDINGNETWORK CONNECTIVITY FOR A WIRELESS TERMINAL,” both of which are herebyexpressly incorporated by reference.

FIELD OF THE INVENTION

The present invention is directed to communication systems, and moreparticularly, to methods and apparatus for supporting communicationbetween a wireless terminal, e.g., mobile node, and multiple basesstations.

BACKGROUND OF THE INVENTION

In a wireless communication system, a wireless terminal, e.g., mobilenode, is often coupled to a wired network, such as the Internet, viabase stations. Base stations provide network connectivity within acoverage area called a cell. The communications path from a base stationto the wireless terminal is called a “downlink”, while a communicationspath from the wireless terminal to a base station is called an “uplink”.

For the purpose of network connectivity, at a minimum, the wirelessterminal communicates with one base station. However, for variousperformance considerations typically in support of terminal mobility,e.g., moving from cell to cell, wireless terminals are often equipped tosimultaneously maintain wireless link connections with multiple basestations. For example, in a Code Division Multiple Access (CDMA) system,the wireless terminal can be in a “soft handoff” state.

FIG. 1 illustrates a known CMDA communications network 100, whichincludes wireless terminal 102, base station 1 104, base station 2 106,mobile switching center 108 and wired networks 110. Variouscommunications between the network elements are represented by arrows.Uplink communications are illustrated in FIG. 1 and downlinkcommunications are illustrated in FIG. 2.

The existing method of soft handoff in direct spread CDMA technologiesdelivers a single data information flow split across multiple linkconnections, each from a different base station, to a wireless terminal,and another data flow from the terminal back to the multiple basestations. The consequent characteristics, including tight timesynchronization of these connections between the base stations and theterminal, constrains the technology choice for use in a radio accessnetwork infrastructure.

Referring to FIG. 1, in the soft handoff state, using the uplink, thewireless terminal 102 transmits a signal 112, 114 representinginformation to be sent. In this example, the wireless terminal 102 is inthe coverage area of more than one base station 104, 106. Therefore,more than one base station 104, 106 listens to the same uplink signal112, 114 simultaneously.

Then, in response to receiving the signal 112, 114 from the wirelessterminal 102, the base stations 104, 106 process received signals. Asrepresented by arrows 116 and 118, the processing results are sent to acentral unit, often referred to as a mobile switching center 108, whichcombines the results from individual base stations 104, 106 to obtainthe sent information. Then the mobile switching center 108 sends theinformation to the wired network 110, e.g., the Internet. This isrepresented by arrow 120.

Similarly, in regard to the downlink, as illustrated in FIG. 2, themobile switching center 108 receives information from the wired networks110 for the wireless terminal 102, as represented by arrow 220. Then themobile switching center 108 duplicates the information and transmits theinformation to more than one base station 104, 106. This is representedby arrows 216, 218. The base stations 104, 106 simultaneously transmitthe received signal representing the information to the wirelessterminal 102. This is shown using arrows 212 and 214. The wirelessterminal 102 combines the signals received from the base stations 104,106 to obtain the information from the wired networks 110.

One advantage of having the soft handoff state is to achieve macrodiversity. In addition, the soft handoff state also reduces data lossand latency during handoff, i.e., when the wireless terminal is switchedfrom one base station to another data is transmitted by multiple basestations.

Data received by a wireless terminal from a first base station can becombined with data received from a second wireless terminal whichtransmits the same signal to form a complete message or set of data evenwhen communication with the first base station is lost, e.g., due toentry into the coverage area of the second base station.

Soft handoff has the disadvantage associated with the complexity andtiming requirements of utilizing mobile switching center 108 as acombining unit in the uplink and as a duplicating unit in the downlink.This characteristic constrains network operations, since thischaracteristic requires synchronized network transport technologycapable of delivering data information to and from the mobile switchingcenter 108 and the base stations 104, 106 with very low delay jitterwith respect to the multiple base stations 104, 106. That is, in suchsystems information to and from the multiple base stations 104, 106 andthe mobile switching center 108 must be tightly synchronized in time.This synchronized-network transport characteristic stands in markedcontrast to the operation of packet-switched data networks thattypically utilize asynchronously-networked transport technologies.

In a mobile communication system, maintaining multiple link connectionssimultaneously is important to ensure seamless handoffs. However, thereare compelling economic advantages in using more asynchronous forms ofdata networking technologies within radio access networks. Accordingly,there is a need for improved methods and apparatus for enabling wirelessconnectivity, at least some of which will allow the wireless terminalsto be simultaneously connected with multiple base stations whileenabling the base stations to communicate with the wired network in away consistent with asynchronous, packet-switched data networking.

SUMMARY OF THE INVENTION

The present invention is directed to methods and apparatus which allow awireless terminal to simultaneously maintain connections with multiplebase stations.

The invention described here allows a wireless terminal to besimultaneously connected with multiple base stations in, e.g., anasynchronous network, yet being able to send different data and/orcontrol information flows in each link connection from each base stationto the terminal, and from the terminal back to the base stations. Inthis way simultaneous yet different information flows are possiblebetween a wireless terminal and multiple base stations. There is norequirement for time synchronization between the link connections of thebase stations communicating with the terminal. Consequently moretechnology options exist for use in the radio access networkinfrastructure.

In accordance with the invention, multiple simultaneous connections areindependently operated. Connections may include each an uplink, adownlink or both an uplink and a downlink. In the physical layer,separate synchronization loops are individually tuned and used for eachof the multiple connections. To facilitate simultaneous operation ofindependent timing synchronization loops used to support simultaneouscommunication with multiple base stations, multiple uplink and multipledown link receiver and timing synchronization circuits, may be includedin each wireless terminal.

In the upper communications layers, the control, e.g., timing and powercontrol signals and data information carried by distinct connections maybe, and typically, are different.

With regard to connections established by a wireless terminal, thewireless terminal and the base stations have the choice of letting a setof downlinks and/or uplinks to be active and keeping the remaining linksinactive. In various embodiments, for an active downlink or uplink, thewireless terminal has the choice of carrying data and/or controlinformation flows on that link.

The wireless terminal is equipped with multiple pairs of transmitter andreceiver circuits, where each transmitter/receiver pair is dedicated fora particular connection. Preferably, a plurality of transmitter/receiverpairs share the same analog device components, e.g.,receiver/transmitter circuitry. In the exemplary embodiment, differentconnections are individually synchronized and separated in the digitaldomain.

A make-before-break handoff method implemented in accordance with theinvention involves a wireless terminal maintaining multiplesimultaneous, independent connections with both current and handoffcandidate base stations before the connection with the current basestation goes down. The connections with both the current and handoffcandidate base stations are independently operated. Duringmake-before-break handoff, the downlinks and uplinks of the multipleconnections may remain active, and all may carry both control and dataflows. However, due to system and/or terminal constraints, theaforementioned handoff behavior may also be restricted such that most orall the downlinks of the multiple connections are active and carry bothcontrol and data flows. While multiple uplinks are active and carrycontrol flows at the same time for a given device, in one exemplaryembodiment a single uplink is used to communicate the device's data flowat any given time.

Numerous additional features, benefits and details of the methods andapparatus of the present invention are described in the detaileddescription which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a known communications system with uplink signalingduring, e.g., a soft handoff.

FIG. 2 illustrates a known communication system with downlink signalingduring, e.g., a soft handoff.

FIG. 3 illustrates a communications system implemented in accordancewith an exemplary embodiment of the present invention.

FIGS. 4-6 illustrate three embodiments of maintaining multiple networkconnections in accordance with the present invention.

FIG. 7 illustrates presence of multiple separate synchronization loops,one for each base station with which the wireless terminal may interactat any given point in time.

FIG. 8 is a block diagram showing an exemplary wireless terminalimplemented in accordance with the present invention in greater detail.

FIG. 9 illustrates transmitter circuitry which may be used as thetransmitter circuitry of the wireless terminal of FIG. 8.

FIG. 10 illustrates receiver circuitry which may be used as the receivercircuitry of the wireless terminal of FIG. 8.

FIGS. 11-14 illustrate the signaling and connections established as partof a make before break operation performed in accordance with thepresent invention.

DETAILED DESCRIPTION

FIG. 3 illustrates a communication system 300 implemented in accordancewith the present invention. Communications system 300 includes wirelessterminal 302, base station 1 304, base station 2 306, and wired networks308. Communications between the system 300 elements are represented byarrows and will be described below.

The wireless terminal 302 is equipped to maintain multiple wirelessconnections with multiple base stations 304, 306 in parallel, e.g.,simultaneously. A wireless connection links the wireless terminal 302with a particular base station, e.g. base station 1 304, and is used toexchange data, network level and higher, and/or control, link and MAClayer, information, i.e., data flow and/or control flow, between thewireless terminal 302 and base station 1 304. In accordance with theinvention the wireless terminal 302 can establish a wireless connectionwith more than one base station, e.g., base station 1 304 and basestation 2 306. The technologies and/or spectrum used by distinctsimultaneous connections can be the same or different.

In accordance with the invention, at any given time, the pieces ofinformation carried by the distinct simultaneous connections between thewireless terminal 302 and the base stations 304, 306, can, and normallyare, different. Therefore the connections that carry differentinformation at the same time are independent connections or in otherwords information is carried on different channels.

FIG. 3 illustrates the two simultaneous and independent connections thewireless terminal 302 makes with the base stations 304, 306. Theseconnections use the same available bandwidth, but use differentcommunications channels so the connections do not interfere with eachother. Arrows 310 and 312 represent the communications channels.

The method of multiple simultaneous independent connections is differentfrom the method of soft handoff because of at least the followingreason. In particular, in accordance with the invention, the signalsexchanged between the wireless terminal 302 and multiple base stations304, 306 carry different pieces of information, while in soft handoffthe signals over the multiple links carry the same pieces ofinformation. Since both channels carry separate information, a mobileswitching center is not needed as a combining and/or duplicating unit.Therefore, in accordance with the invention, the base stations 304, 306can be coupled to the wired networks 308 directly, individually andindependently. This is represent in FIG. 3 by arrows 314 and 316.

A connection or channel is comprised of a pair of separatecommunications paths, a downlink and an uplink each of which carriesseparate information flows. The downlink, the uplink or both are activefor a connection at any given time. Moreover, when a downlink or uplinkis active, data and/or control signals, flows, are transmitted over theconnection.

In accordance with the invention, the activities of distinct connectionscan be different, and when active, the types of information flowstransmitted over distinct connections can be different. During any giventime period in which multiple connections exist with a given wirelessterminal 302, either the wireless terminal 302 or the base stations 304,306 have the choice of dynamically setting a set of downlinks and/oruplinks to be active and, optionally, keeping the remaining inactive.For an active downlink or uplink, either the wireless terminal or thebase stations have the choice of carrying data and/or control flows onthat link. Various embodiments for connections settings will now bedescribed.

FIGS. 4-6 illustrates three embodiments of the present inventionimplemented with the base stations 1 and 2 304, 306 of communicationssystem 300. Control flows are represented by dashed lines and data flowsare represented by solid lines. Active downlinks or uplinks arerepresented by arrows heads in the appropriate direction, i.e., pointingtowards the wireless terminal for downlinks and pointing towards thebase station for uplinks.

In the first embodiment, illustrated in FIG. 4, the wireless terminal302 has connections 410, 414 with first and second base stations 304,306, respectively. Each connection 410, 414 includes a control uplink408, 412 and a control downlink 409, 413, respectively. Each connection410, 414 also includes a data uplink 416, 418 and a data downlink 41,419, respectively. Accordingly, in the FIG. 4 example, bi-directionalcontrol and data communications is supported for communications withboth base stations 304, 306.

In a second embodiment of the present invention, illustrated in FIG. 5,the wireless terminal 302 has connections 510, 514 with first and secondbase stations 304, 306, respectively. Each of the first and secondconnections 510, 514 includes a control uplink 508, 512 and a controldownlink 509, 513, respectively. The first connection 510 also includesa data uplink 516 and a data downlink 517. The second connection 514includes a data downlink 519 but no data uplink. Accordingly, in theFIG. 4 example, bi-directional control signaling is supported for boththe connections with both base stations 304, 306, bi-directional datacommunication is supported with one base station 304 while downlink datacommunications is supported for the connection 514 with the second basestation 306.

As illustrated in FIG. 5, base station 1 304 has both uplink (508, 516)and downlink (509, 517) connections with wireless terminal 502 whichcarry control and data flows. On the other hand, with base station 2306, has both an uplink 512 and a downlink 513 connection for controlflows, but only downlink connection 519 for data flows. In the FIG. 5example, a single uplink is used by a device to transmit data at anygiven time despite the existence of multiple active uplinks any or allof which may be used to communicate control information.

In a third example of the present invention, illustrated in FIG. 6, atany given point in time, each of the wireless terminal's connections610, 614 includes active control (609, 613) downlinks and active data(613, 619) downlinks, while a single one of the wireless terminal'sconnections 610, 614 includes both an active control uplink 608 andactive data uplink 616. In this manner, the wireless terminal can fullyinteract with one base station 304 at a given time but receive controland data signals from multiple base stations 304, 306.

For example wireless terminal 602 has an active control and datadownlinks (609, 617) and uplinks (608, 616) with base station 1 304,thereby allowing bi-directional communication of both of the connectioncarry control and data flows. On the other hand for base station 2 306,the wireless terminal 302 has active downlinks 613, 619 for control anddata flows, respectively, but no active uplink connection.

For a connections to be established, the wireless terminal 302 and thecorresponding base stations 304, 306 to which the terminal 302 is to beconnected are synchronized to each other, where the synchronizationoperation typically involves carrier frequency and symbol/frame timingsynchronization. In the case where the base stations 304, 306 are notsynchronized themselves, in accordance with the invention, thesynchronization operations for individual connections 310, 312 areindependently carried out.

Specifically, the carrier frequency and symbol/frame timing parametersat both transmitter and receiver of the wireless terminal 302 areindependently set and/or tuned for individual connections 310, 312. FIG.7 illustrates the use of separate synchronization control loops 704, 706within the wireless transmitter 302 to insure proper, independent timingsynchronization with each of the base stations 304, 306 to which thewireless terminal 302 is connected.

In the FIG. 7 example, wireless terminal 302 has first and secondindependent, e.g., asynchronous, connections 310, 312. The firstconnection 310 is with base station 1 304 while the second connection312 is with base station 2 306. Since the base stations 304, 306 are notsynchronized, the wireless terminal 302 maintains separatesynchronization loops 704, 706 for each connection. Synchronization loop1 704 is for the first connection 1 310 while the second synchronizationloop 706 is for the second connection 312. While synchronization loops704, 706 function independently, they may share some common hardware,e.g., analog receiver circuitry, used to receive signals correspondingto connections 310, 312 while independent digital processing may be usedto perform all or a portion of the timing control implemented in each ofthe synchronization loops 704.

FIG. 8 illustrates an exemplary wireless terminal 302 of the presentinvention in greater detail than the preceding figures. The wirelessterminal includes a transmitter antenna 752 that it coupled totransmitter circuitry 754. It also includes a receiver antenna 756 thatis coupled to receiver circuitry 758. Transmitter circuitry 754 receivesdigital control and data signals to be transmitted from bus 767.Receiver circuitry 758 generates digital control and data signals fromreceived signals which are output over bus 767. Transmitter and receivercircuitry are responsive to timing, power control, and other signalsreceived from other terminal components via bus 767.

Bus 767 couples various components of the wireless terminal together asshown in FIG. 8. The components that are coupled together include aninput device 770, an output device 772, transmitter circuitry 754,receiver circuitry 758, a processor, e.g., CPU, 774 and memory 760.Input device may be, e.g., a keypad and/or microphone. Output device 772may include a speaker and/or display device. Memory 760 includes data760, e.g., voice, text, E-mail or other types of data, stored in theform of files, which has been received or is to be transmitted. The datamay be stored as packets or packetized prior to transmission. Memoryalso includes transmission routines 764, reception routines 766 anddifferent sets of parameters 777, 779 for each connection with a basestation that is maintained. Transmission routines 764 and receptionroutines 766 are executed by processor 774 and control varioustransmission/reception operations. Transmission routines 764 may includea synchronization loop routine and a main digital processing routinethat can be executed for each base station connection that is to besupported by the wireless terminal 302 at any given time to provide,when executed, a synchronization loop and a main digital processingmodule (see, e.g., FIG. 9). Similarly, reception routines 766 may alsoinclude a synchronization loop routine and a main digital processingroutine that can be executed for each base station connection that is tobe supported by the wireless terminal 302 at any given time to provide,when executed, a synchronization loop and a main digital processingmodule (see, e.g., FIG. 10).

Transmission routines 764 and reception routines 766 are executed byprocessor 774 and control various transmission/reception operations.Under control of the routines 766, 774 the processor circuitry 774 mayis configured to operate as receiver and transmitter synchronizationloop circuits and receiver/transmitter main digital processing modules.Alternatively, such circuits and/or modules may be implemented usingdedicated hardware circuits.

Transmitter and receiver systems that use these multiple synchronizationloops will now be described.

The wireless terminal 302 is equipped with multiple transmitter andreceiver pairs, where each pair is dedicated for a particularconnection. In one embodiment of the invention, individualtransmitter/receiver pairs are constructed with separate devicecomponents. An exemplary transmitter system 800 is described withrespect to FIG. 8 and an exemplary receiver system 900 is described withrespect to FIG. 9.

FIG. 9 illustrates wireless terminal components 800 used fortransmitting signals to base stations in accordance with the presentinvention. The wireless terminal components 800 include an analogprocessing module 814, a Digital-to-Analog converter (DAC) 812, anadding unit 810, synchronization loops 806, 808 and main digitalprocessing modules 802, 804, coupled together as shown in FIG. 8. Analogprocessing module 814, D/A converter 812 and adding unit 810 may be partof the transmitter circuitry 754 shown in FIG. 8. Synchronization loops806, 808 and digital processing modules 802, 804 may be implemented byexecuting routines 764 on processor 774 or by using dedicated hardwarecircuits. Analog processing module 814 may include elements such asRadio Frequency (RF) and analog filters, analog mixers, etc. The signalstransmitted to base stations 304 and 306 are processed by each of thesecircuits. However, such circuits could be duplicated for transmission toeach of the base stations 304, 306 avoiding the need for adding unit 810but requiring multiple modules 814 and D/A converters 812.

In an exemplary transmission operation, the digital signalscorresponding to different base station connections are first generated,where each signal represents the control and/or data information to besent on the corresponding connection. The signals may be generated byprocessor 774. In accordance with the invention, the digital signals tobe transmitted to each base station are independently processed byseparate main digital processing modules 802, 804 and synchronizationloops 806, 808 used for processing signals directed to base station towhich the signals are directed. In the FIG. 8 example, the digitalsignals to be transmitted over the different connections are furtherdigitally processed, e.g., channel encoded, by main digital processingmodules 802, 804.

Base stations may not be synchronized. Therefore, in accordance with theinvention, for the synchronization purposes frequency and timingcorrections are carried out independently, based on the synchronizationparameters, using digital signal processing for the digital signals ofindividual connections. These frequency and timing correction areindependently performed on a per base station connection basis by thesynchronization loops 806, 808.

The separated digital signals to be transmitted to the base stations304, 306 are then added and converted to a single analog signal byadding unit 810 and DAC 812, respectively. The information on thedifferent connections is carried on separate communications channels,e.g., OFDM communications channels implemented using, e.g., differentfrequency tones. Therefore the adding unit introduces minimal interfaceto the information to be sent when the information is combined. Theconverted analog signal is amplified and then transmitted over thewireless channel by analog processing module 814.

FIG. 10 illustrates wireless terminal components 900 used for receivingsignals from base stations in accordance with the present invention. Thewireless terminal components 900 include an analog processing module902, an Analog-to-Digital converter (ADC) 904, a duplicating unit 906,signal separator circuits 905, 907, synchronization loops 908, 910 andmain digital processing modules 912, 914, coupled together as shown inFIG. 10. Analog processing module 902 may include elements such as RadioFrequency (RF) and analog filters, analog mixers, etc. Analog processingmodule 902, A/D converter 904 duplicating unit 906, and signal separatorcircuits 905, 907 may be implemented as part of the receiver circuitry758. Synchronization loops 908, 910 and digital processing modules 912,914 may be implemented by executing routines 766 on processor 774 or byusing dedicated hardware circuits.

In exemplary receiver operation, received signals, e.g., analog signals,are first processed by analog device components, e.g., analog filters,amplifiers, by analog processing module 902. Then, the processed signalis converted to a single digital signal by ADC 904. The digital signalis then duplicated, by duplicating unit 906, to form multiple copies ofthe same digital signal. Each of the multiple copies of digital signalsis further processed on a per base station connection.

In accordance with the invention, the receiver system 900 includesseparate signal separator circuits 905, 907, synchronization loops 908,910 and main digital processing modules 912, 914 for each of its basestation 310, 312 connections. For synchronization purposes frequency andtiming corrections are independently carried out for the digital signalsof individual connections based on synchronization parameters and byperforming digital signal processing operations after signal separationis done by one of circuits 905, 907. In this example, the separation ofthe corresponding connections is carried out in the digital domain.

The signal separation, timing synchronization and decoding operationsare performed by signal separation circuit 905, 907, the synchronizationloop 908, 910 and the main digital processing module 912, 914,corresponding to each base station connection. Accordingly signalscorresponding to different base stations are processed independently inthe digital domain.

The main digital processing performed by modules 912, 914 may include,e.g., channel decoding operations. As the result of decoding performedby modules 912, 914 the transmitted data and/or control signalscorresponding to each individual base station are separately recovered.The recovered control and/or data information is stored in the memory810 and/or subject to further processing by processor 824.

In accordance with various implementations of the present invention, aplurality of transmitter/receiver pairs can share the same analog devicecomponents, such as Radio Frequency (RF) and analog filters.

One situation where a wireless terminal 302 may maintain connectionswith multiple base stations is during a handoff operation. In accordancewith the invention, when a wireless terminal 302 is performing a handoffoperation, it maintains multiple simultaneous independent connectionswith the base stations 304, 306 in the neighboring area. An exemplaryhandoff operation will now be discussed with respect to thecommunication system of FIG. 3.

Wireless terminals may move and, as a result, encounter new basestations within their transmission range. When a wireless terminal 302detects the presence of a new base station, e.g., base station 2 306,and determines the new base station 306 is a handoff candidate, itestablishes a new connection with the new base station 306. This is doneby either directly communicating with the new base station 306, e.g.,providing device specific connection setup information to the new basestation 306 and/or by indirectly communicating with the new basestation, e.g., having the current serving base station 304 inform thenew base station 306 of the presence or wireless terminal 302 in the newbase station's coverage area.

Preferably, in the handoff operation, the new connection is establishedbefore the connection with the current base station 304 goes down,resulting in the make-before-break feature of the handoff operation. Themake-before-break feature effectively reduces or even eliminates thedata loss and latency that might otherwise occur during a handoff.

FIGS. 11-14 illustrate the connections established as part of amake-before-break handoff operation of the present invention. In theexample in FIGS. 11-14 bi-directional control and data communicationslinks are supported. The wireless terminal maintains an active uplinkfor each base station with which it communications. The uplinks are usedto transmit control information, such as power control and link layeracknowledgment, to individual base stations. In accordance with theinvention, those pieces of control information can be different fordifferent base stations.

FIG. 11 illustrates step 1 of a handoff. In this step, the wirelessterminal 302 has one connection to a base station, e.g., the first basestation 304. The connection carries control information on link 1010 anddata information on link 1008 in both uplink and downlink directions.

As the wireless terminal 302 moves closer to base station 2 306, in step2, the wireless terminal 302 decides to add base station 2 306 as ahandoff candidate. Therefore, as illustrated in FIG. 12, the wirelessterminal 302 establishes and maintains two connections, one with thefirst base station 304 and another with the second base station 306.

In accordance with the present invention the two connections areindependently operated. For this exemplary embodiment, in the downlink,different data packets and control information are received from each ofthe first and second base stations 304, 306. The data packets receivedby the different base stations 304, 306 may be different parts of thesame file or message, e.g., voice E-mail or text message, which is beingtransmitted. In the uplink, control information is transmitted to bothbase stations 304, 306, as represented by the upward facing arrowheadson arrows 1010 and 1112. The control information transmitted todifferent base stations 304, 306 can be different, e.g., since the basestations may not be synchronized. That is, in some embodiments,different symbol transmission start times are used by each base station304, 306 requiring different symbol timing synchronization to beperformed in regard to signals exchanged with the different basestations 302, 304.

In the example shown in FIG. 12, data packets, are transmitted from thewireless terminal to a single base station, e.g., the first base station304, at any given time. The single base station to which the wirelessterminal 302 transmits its uplink data flow is preferably the one havingthe best wireless channel condition. For example, suppose that basestation 1 304 has the best wireless channel condition. Therefore, thewireless terminal 302 will transmit the data packets through the linkconnection 1008 to the base station 304.

Now suppose that the wireless channel condition of second base station306 becomes better than that of first base station 304. The wirelessterminal 302 will switch to the second base station 306 for datatransmission purposes and will transmit the data packets through theconnection with the second base station 306 instead of the connectionwith first base station 304.

When making the switch there can be an overlapping period of time. Inthis time the benefits of having two connections are evident. Forexample, the wireless terminal 302 may continue to transmit its dataflows to first base station 304 in order to finish serving the datapackets, which are in the middle of transmission, while the data flowsof new, different data packets to the second base station 306, alsostart. The different data packets transmitted to the first and secondbase stations 304, 306 may include, e.g., IP packets representingdifferent portions of the same message or file. The simultaneous datatransmissions to two base stations 304, 306 is possible because the twoconnections are over two different communications channels.Alternatively, the wireless terminal 302 can first finish serving thedata packets that are in the middle of transmission to the first basestation 304, and then start the data flows of new data packets to secondbase station 2 306.

As channel conditions for the connection to the second base station 306improve over channel conditions for the connection to the first basestation 304, e.g., as the wireless terminal moves from one cell toanother, in a third step, the wireless terminal 302 will initiate aswitch of its data flow from the first base station 304 to the secondbase station 306. This results in connections and signal flows asillustrated in FIG. 13. In FIG. 13, the wireless terminal's uplink dataflow connection with the first base station 304 has been terminated andwireless terminal 302 has formed an uplink data flow connection 1210with the second base station 306. Accordingly, with the start of thetransmission of data to the second base station 306, the flow of data tothe first base station 304 will stop. In this embodiment, at a giventime, a single uplink connection is used to carry the data flow, whileall active uplink connections carry the control flows. Active uplinkcontrol flows are represented in FIG. 13 by upward facing arrowheads onconnections 1209 and 1211.

As the wireless terminal 302 moves out of range of the first basestation 304, the corresponding connection 1208, 1209 is torn down instep 4 of a handoff of the present invention. As a result, as shown inFIG. 14, the wireless terminal 302 will have one connection 1210, 1211to the second base station 306. Thus, at the end of the handoffoperation, the mobile node 302 will have a single connection with the abase station.

The make-before-break handoff is fundamentally different from the softhandoff, in that the multiple simultaneous connections between awireless terminal and different base stations are independent and thatthey carry different control and./or data information. In accordancewith the invention, the connections with both the current and the newbase stations are independently operated.

Specifically, in the physical layer, and in the wireless terminal'smemory 760, the wireless terminal maintains separate sets oftransmitter/receiver synchronization parameters 777, 779 for thedifferent connections. Moreover, in the upper layers, the pieces ofinformation carried on the connections for different base stations maybe different. In the downlink direction, the data and control flows fromthe base stations to the wireless terminal may contain different piecesof information. For example, the base stations can, and in variousembodiments do, send different independent data packets to the wirelessterminal simultaneously. Similarly, in the uplink direction, the dataand control flows from the wireless terminal to the base stations mayalso include different pieces of information.

The steps of the various methods of the present invention may beimplemented in a variety of ways, e.g., using software, hardware or acombination of software and hardware to perform each individual step orcombination of steps discussed. Various embodiments of the presentinvention include means for performing the steps of the various methods.Each means may be implemented using software, hardware, e.g., circuits,or a combination of software and hardware. When software is used, themeans for performing a step may also include circuitry such as aprocessor for executing the software. Accordingly, the present inventionis directed to, among other things, computer executable instructionssuch as software for controlling a machine or circuit to perform one ormore of the steps or signal processing operations discussed.

The timing synchronization loops of the present invention may beimplemented using various techniques and/or circuits. U.S. patentapplication Ser. No. 10/090,871 filed Mar. 4, 2002 titled “Method ofSymbol Timing Synchronization in Communication Systems” and U.S. patentapplication Ser. No. 09/503,040 filed Feb. 11, 2000, both of which arehereby expressly incorporated by reference, describe various timingsynchronization circuits and techniques that may be used to implementthe timing loops used in a wireless terminal of the present invention.However, alternative techniques and/or circuits may be used.

It is to be understood that numerous variations on the above describedmethods and apparatus are possible without departing from the scope ofthe invention. For example, the invention was explained in terms of awireless terminal establishing connections with two base stations. Inaccordance with the invention simultaneous connections between awireless terminal and any number of base stations may be established andmaintained. In addition, embodiments where a wireless terminal (303)supports multiple data uplinks with different base stations (304, 306)at the same time but a single data downlink at any given time arecontemplated. Such data links would be in addition to control links,e.g., bidirectional control links, with both base stations. Such animplementation would be similar to the one shown in FIG. 5 but with thearrow 519 reversed to represent an uplink instead of a downlink.

It is also to be understood that while the methods and apparatus of thepresent invention are suitable for orthogonal frequency divisionmultiplexed (OFDM) applications, they can be used with othercommunications techniques as well and are not limited to OFDM systems.

What is claimed is:
 1. A wireless terminal for communicating with aplurality of base stations, comprising: a processor; and circuitrycoupled to said processor configured to: establish a first connectionbetween the wireless terminal and a first base station; receive firstdata and first control information from the first base station via thefirst connection; establish a second connection between the wirelessterminal and a second base station; receive second data and secondcontrol information from the second base station via the secondconnection, and maintain the second connection in parallel with thefirst connection; wherein the second data is received in parallel withthe first data, wherein the second data is different from the firstdata, wherein the second control information is received in parallelwith the first control information, wherein the first controlinformation is different from the second control information, thecircuitry also being configured to perform first synchronizationoperations for the first connection, and perform second synchronizationoperations for the second connection; begin transmission of a first datapacket to the first base station; finish transmission of the first datapacket to the first base station in parallel with starting transmissionof a second data packet to the second base station, wherein the firstdata packet and the second data packet comprise different data; anddetermine that wireless channel conditions for the second base stationare better than wireless channel conditions for the first base station,and wherein the transmission of the second data packet to the secondbase station is started in response to making this determination.
 2. Thewireless terminal of claim 1, wherein the first and secondsynchronization operations comprise frequency synchronizationoperations.
 3. The wireless terminal of claim 1, wherein the first andsecond synchronization operations comprise symbol timing synchronizationoperations.
 4. The wireless terminal of claim 1, wherein the first datapacket and the second data packet comprise different parts of a singledata file.
 5. The wireless terminal of claim 1, wherein the circuitry isfurther configured to use different symbol transmission start times whentransmitting symbols representing at least portions of the first andsecond data packets to the first and second base stations.
 6. Thewireless terminal of claim 1, wherein the circuitry is furtherconfigured to discontinue transmitting data to the first base stationafter transmission of the first data packet is complete.
 7. The wirelessterminal of claim 1, wherein the circuitry is further configured toseparate a first received signal comprising the first data and the firstcontrol information from a second received signal comprising the seconddata and the second control information.
 8. The wireless terminal ofclaim 1, wherein the circuitry is further configured to: determine,after the transmission of the first data packet has started and beforethe transmission of the first data packet has completed, that thewireless channel conditions for the second base station are better thanthe wireless channel conditions for the first base station.
 9. A methodfor communicating with a plurality of base stations, the method beingimplemented by a wireless terminal, the method comprising: establishinga first connection between the wireless terminal and a first basestation; receiving first data and first control information from thefirst base station via the first connection; establishing a secondconnection between the wireless terminal and a second base station;receiving second data and second control information from the secondbase station via the second connection; maintaining the secondconnection in parallel with the first connection, wherein the seconddata is received in parallel with the first data, wherein the seconddata is different from the first data, wherein the second controlinformation is received in parallel with the first control information,and wherein the first control information is different from the secondcontrol information; performing first synchronization operations for thefirst connection; performing second synchronization operations for thesecond connection; beginning transmission of a first data packet to thefirst base station; finishing transmission of the first data packet tothe first base station in parallel with starting transmission of asecond data packet to the second base station; and determining thatwireless channel conditions for the second base station are better thanwireless channel conditions for the first base station, and wherein thetransmission of the second data packet to the second base station isstarted in response to making this determination.
 10. The method ofclaim 9, wherein the first and second synchronization operationscomprise frequency synchronization operations.
 11. The method of claim9, wherein the first and second synchronization operations comprisesymbol timing synchronization operations.
 12. The method of claim 9,wherein the first data packet and the second data packet comprisedifferent parts of a single data file.
 13. The method of claim 9,further comprising using different symbol transmission start times whentransmitting symbols representing at least portions of the first andsecond data packets to the first and second base stations.
 14. Themethod of claim 9, further comprising discontinuing transmitting data tothe first base station after transmission of the first data packet iscomplete.
 15. The method of claim 9, further comprising separating afirst received signal comprising the first data and the first controlinformation from a second received signal comprising the second data andthe second control information.
 16. A wireless terminal forcommunicating with a plurality of base stations, comprising: means forestablishing a first connection between the wireless terminal and afirst base station; means for receiving first data and first controlinformation from the first base station via the first connection; meansfor establishing a second connection between the wireless terminal and asecond base station; means for receiving second data and second controlinformation from the second base station via the second connection;means for maintaining the second connection in parallel with the firstconnection, wherein the second data is received in parallel with thefirst data, wherein the second data is different from the first data,wherein the second control information is received in parallel with thefirst control information, and wherein the first control information isdifferent from the second control information; means for performingfirst synchronization operations for the first connection; means forperforming second synchronization operations for the second connection;means for beginning transmission of a first data packet to the firstbase station; means for finishing transmission of the first data packetto the first base station in parallel with starting transmission of asecond data packet to the second base station; and means for determiningthat wireless channel conditions for the second base station are betterthan wireless channel conditions for the first base station, and whereinthe transmission of the second data packet to the second base station isstarted in response to making this determination.
 17. The wirelessterminal of claim 16, wherein the first and second synchronizationoperations comprise frequency synchronization operations.
 18. Thewireless terminal of claim 16, wherein the first and secondsynchronization operations comprise symbol timing synchronizationoperations.
 19. The wireless terminal of claim 16, wherein the firstdata packet and the second data packet comprise different parts of asingle data file.
 20. The wireless terminal of claim 16, furthercomprising means for using different symbol transmission start timeswhen transmitting symbols representing at least portions of the firstand second data packets to the first and second base stations.
 21. Thewireless terminal of claim 16, further comprising means fordiscontinuing transmitting data to the first base station aftertransmission of the first data packet is complete.
 22. The wirelessterminal of claim 16, further comprising means for separating a firstreceived signal comprising the first data and the first controlinformation from a second received signal comprising the second data andthe second control information.
 23. A non-transitory computer-readablemedium for facilitating communication between a wireless terminal and aplurality of base stations, the computer-readable medium havinginstructions stored thereon, the instructions being executable to:establish a first connection between the wireless terminal and a firstbase station; receive first data and first control information from thefirst base station via the first connection; establish a secondconnection between the wireless terminal and a second base station;receive second data and second control information from the second basestation via the second connection; maintain the second connection inparallel with the first connection, wherein the second data is receivedin parallel with the first data, wherein the second data is differentfrom the first data, wherein the second control information is receivedin parallel with the first control information, and wherein the firstcontrol information is different from the second control information;perform first synchronization operations for the first connection;perform second synchronization operations for the second connection;begin transmission of a first data packet to the first base station;finish transmission of the first data packet to the first base stationin parallel with starting transmission of a second data packet to thesecond base station; and determine that wireless channel conditions forthe second base station are better than wireless channel conditions forthe first base station, and wherein the transmission of the second datapacket to the second base station is started in response to making thisdetermination.
 24. The computer-readable medium of claim 23, wherein thefirst and second synchronization operations comprise frequencysynchronization operations.
 25. The computer-readable medium of claim23, wherein the first and second synchronization operations comprisesymbol timing synchronization operations.